i thought I would start a thread specifically for this card, as it's referred to as parts of other projects - mylesgm, JLMaudio and sodderboy have posted related threads, but will focus here on working specifically with elements and applications.
I have a 10852 line amp card, and have been working with it as a test rig to explore DIY.
the first iteration, i used the mix inputs and a 15v power supply, and it worked nicely.
i decided to take things further as I learned more, and got a JLM AC/DC power supply (thanks Joe) to provide the correct +/- 25V power. I've also recapped the board, and am now using it as a virtual-earth gain make up amp for a very simple 8-channel stereo summing matrix. No pans, axes, just 4 channels, balanced hard left & right, using 10K resistors.
I'm currently working on lowering the noise floor, getting the grounding right, etc.
As an aside, I purchased Geoff Tanner's Technical Notes and have found them hugely helpful, and would recommend to anyone exploring DIY.
I'll note some observations and questions, which hopefully will be helpful to anyone else exploring this card. I'll put the questions in bold.
The card has separate connections for input & output return, which I take to mean ground/0 V reference, and if anyone could illuminate:
What's the best approach to grounding this card in a stand-alone DIY application?
Geoff mentioned in an earlier post that this console series (51-xx) introduced a new system of grounding, and a 'quasi-balanced' mix buss architecture - would love to hear more about this.
With only 4 inputs, the bus impedance is fairly high on the summing network. I'm taking the + sum to the non-inverting input, and the - sum to the inverting input, both of which feed differential transistors. It works, but the summing matrix is very susceptible to induced noise. I switched to screened cables inside the chassis from the matrix to the amp inputs, and it made a big difference. I thought that by using the VE inputs, the buss impedance would not be as important to bring down with a shunt resistor, so not using one currently.
Should I use a shunt resistor to lower the bus impedance to improve noise performance?
What would be the optimal input impedance for this amp?
Would a transformer at this stage provide any benefits? Perhaps a 10K/600r or variant.
The applications guide for this amplifier notes that when using the VE inputs, a certain resistor ( which doesn't match the issue number of my card) should be replaced with a wire link to improve noise performance. Any thoughts as to why?
Also, the make-up gain of the amplifier is determined by an external feed-on resistor. It seems that the circuit has a default value if nothing is connected here, and I haven't changed or added any values here.
If the feed-on resistor is a potentiometer/variable resistor, could this function as a gain control?
That's all for now - this little unit is quite fun & rewarding to play with, as a matched discrete amplifier and transformer combination. Sounds come alive in here, and since they seem to be around for currently reasonable money, it's been a good start for DIY playing. It seems that the rest of the console had its issues, but this component is quite flexible in what you can do with it, although I don't think trying to make a mic-pre from it makes much sense. Hope this info is helpful, I've learned a lot from this forum.
I have a 10852 line amp card, and have been working with it as a test rig to explore DIY.
the first iteration, i used the mix inputs and a 15v power supply, and it worked nicely.
i decided to take things further as I learned more, and got a JLM AC/DC power supply (thanks Joe) to provide the correct +/- 25V power. I've also recapped the board, and am now using it as a virtual-earth gain make up amp for a very simple 8-channel stereo summing matrix. No pans, axes, just 4 channels, balanced hard left & right, using 10K resistors.
I'm currently working on lowering the noise floor, getting the grounding right, etc.
As an aside, I purchased Geoff Tanner's Technical Notes and have found them hugely helpful, and would recommend to anyone exploring DIY.
I'll note some observations and questions, which hopefully will be helpful to anyone else exploring this card. I'll put the questions in bold.
The card has separate connections for input & output return, which I take to mean ground/0 V reference, and if anyone could illuminate:
What's the best approach to grounding this card in a stand-alone DIY application?
Geoff mentioned in an earlier post that this console series (51-xx) introduced a new system of grounding, and a 'quasi-balanced' mix buss architecture - would love to hear more about this.
With only 4 inputs, the bus impedance is fairly high on the summing network. I'm taking the + sum to the non-inverting input, and the - sum to the inverting input, both of which feed differential transistors. It works, but the summing matrix is very susceptible to induced noise. I switched to screened cables inside the chassis from the matrix to the amp inputs, and it made a big difference. I thought that by using the VE inputs, the buss impedance would not be as important to bring down with a shunt resistor, so not using one currently.
Should I use a shunt resistor to lower the bus impedance to improve noise performance?
What would be the optimal input impedance for this amp?
Would a transformer at this stage provide any benefits? Perhaps a 10K/600r or variant.
The applications guide for this amplifier notes that when using the VE inputs, a certain resistor ( which doesn't match the issue number of my card) should be replaced with a wire link to improve noise performance. Any thoughts as to why?
Also, the make-up gain of the amplifier is determined by an external feed-on resistor. It seems that the circuit has a default value if nothing is connected here, and I haven't changed or added any values here.
If the feed-on resistor is a potentiometer/variable resistor, could this function as a gain control?
That's all for now - this little unit is quite fun & rewarding to play with, as a matched discrete amplifier and transformer combination. Sounds come alive in here, and since they seem to be around for currently reasonable money, it's been a good start for DIY playing. It seems that the rest of the console had its issues, but this component is quite flexible in what you can do with it, although I don't think trying to make a mic-pre from it makes much sense. Hope this info is helpful, I've learned a lot from this forum.
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